1. Field of the Invention
The present invention relates to a semiconductor device and, more particularly, to a semiconductor device including memory cells.
2. Discussion of Related Art
A flash memory device is a typical semiconductor device that has nonvolatile memory cells. Data is stored in memory cells by an increment step pulse program (ISPP) method, which includes a program operation and a verification operation. Specifically, a threshold voltage of the memory cell is changed by the program operation depending on the data programmed and stored therein.
A loss of data (i.e. charge) may occur in a programmed memory cell. Even when the threshold voltage of a programmed memory cell reaches the target voltage during the verification operation, the threshold voltage may drop below the target voltage due to charge leakage. A memory cell that has lost its charge may also be referred to as an under programmed cell.
If the threshold voltage of the memory cell changes due to unintended charge leakage, data stored in the memory cell may change, resulting in an error.